Insensitive propellant composition

ABSTRACT

The present invention relates to a propellant composition which comprises hydroxy-terminated polyether (HTPE), N-butyl-(2-nitratoethyl)nitramine (BuNENA) and ammonium perchlorate (AP) and is insensitive to impact and thermal reactions and thus suitably used for a solid rocket propulsion unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2011-0020788 filed on Mar. 9, 2011, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a propellant composition which comprises hydroxy-terminated polyether (HTPE), N-butyl-(2-nitratoethyl)nitramine (BuNENA) and ammonium perchlorate (AP) and is insensitive to impact and thermal stimulus and thus suitably is used for a solid rocket propulsion unit.

BACKGROUND OF THE INVENTION

Propulsion units, depending on their dimensions, casing types and propellant characteristics, exhibit different reactions to shock or heat applied from outside. It would be ideal if propulsion units do not show any reactions to shock or heat applied from outside, however they show any of reactions such as burning, deflagration, explosion or detonation.

There are techniques for desensitizing a solid rocket propulsion unit so as to reduce such reactions to shock or heat applied from outside, which can be largely classified as techniques regarding a casing and techniques regarding propellant formulations. By properly combining such two techniques together, desired reaction in a propulsion unit may be achieved.

For manufacturing a solid rocket propulsion unit insensitive to bullet impact or bullet fragment impact, a propellant should satisfy 15 MPa/ms or less in the friability test according to UN test series 7(c)(ii) or class 1.3 in a large scale card gap test (LSGT) which has been developed by US Naval ordnance laboratory (NOL).

Further, for manufacturing a thermally insensitive solid rocket propulsion unit, the propellant should satisfy 2 or less (excluding top and bottom lids) in number of broken pieces of metal pipe, when it is subjected to a EIDS slow cook-off (SCO) test according to UN test series 7(f).

Currently, one of the most widely used propellants in rocket industry is hydrorxy-terminated polybutadiene (HTPB)/AP, which is majorly used, to the proportion of 80-90% in conventional solid rocket propulsion unit manufacture. AP has a higher combustion rate which increases as the temperature increases, than other oxidizers or molecular explosives. Further, the natural ignition temperature of AP is more than 250° C., which is relatively higher than that of a nitrate ester plasticized polyether (NEPE) propellant. Near the natural ignition temperature, a binder and AP becomes porous and thus combustion area exponentially increases. For ensuring the performance of the HTPB/AP propellant, the AP content should be high (69-86%). In the HTPB binder, a crosslinking reaction from double-bonds therein is generated which causes increase in brittleness as well as decomposition or vaporization of the components, leading to cracks in the binder. For these reasons, the HTPB/AP propellant is intrinsically disadvantageous to SCO test. Such HTPB/AP propellant with insensitive characteristics shows good results in friability test and LSGT properties, however it does not pass the SCO test. In summary, HTPB/AP propellant shows good results in a bullet impact test, a fragment impact test and fast cook-off test, but its properties tested in SCO are not good enough.

In the meantime, currently there have not been any insensitive oxidizers which can replace AP as a solid propellant oxidizer with satisfying performances. Therefore, there have been needs for an insensitive propellant with improved SCO properties while using AP, so that it can replace a conventional HTPB/AP propellant in industrial or military field.

OBJECT OF THE INVENTION

The object of the present invention, which has been designed to solve the problems of prior arts, is to provide a novel solid propellant composition which is insensitive to impact and thermal stimulus and is suitably used for a solid rocket propulsion unit, specifically to provide a sold propellant composition which has class 1.3 in LSGT, 15 MPa/ms or less in a friability test and improved SCO properties.

DETAILED DESCRIPTION OF THE INVENTION

The insensitive solid propellant composition according to the present invention, in order to achieve the above objects, is characterized by comprising: 5-10 wt % of at least one selected from hydroxy-terminated polyether (HTPE) and hydroxy-terminated polycaprolactone ether (HTPC) as a binder; 5-15 wt % of N-butyl-N-(2-nitratorethyl)nitramine (BuNENA) as a plasticizer; 10-70 wt % of ammonium perchlorate (AP) as a main oxidizer; 1-30 wt % of ammonium nitrate (AN) as an auxiliary oxidizer; and 1-30 wt % of at least one selected from Al compounds, Zr compounds, B compounds and Fe compounds.

For the prepolymer elements, HTPE and HTPC used as a binder in the solid propellant composition according to the present invention, any HTPE and HTPC may be used without being specifically limited. HTPE and HTPC may be used together in the solid propellant composition according to the present invention.

Specifically, HTPC has some advantages over HTPE which is currently used only for military applications, such as low price of raw materials and sufficient supply owing to its commercial use in various industrial applications. Further, the polymer backbone chain of HTPC is composed of caprolactone which allows it to be decomposed by hydrolysis after its aging, thereby being environmentally friendly.

The binder used in the present invention may be used at the amount of 5-10 wt % in the solid propellant composition according to the present invention. When the amount is less than 5 wt %, the mechanical properties of the propellant at high temperature may be disadvantageously degraded, and when it is more than 10 wt %, propellant viscosity may be increased, which is undesirable in terms of manufacturing process for propulsion units.

When HTPE and HTPC are used together, HTPC is preferably used at 10-60 wt % based on the total weight of the binders. When HTPC is used at least 10 wt % based on the total weight of the binders, it is possible to obtain effects anticipated from HTPC which include reduction in cost for manufacturing a propellant and decomposition by hydrolysis after its aging, and when the amount of HTPC used is more than 60% based on the total weight of the binders, the best physical properties of HTPE and excellent affinity for a plasticizer cannot be obtained.

BuNENA which is used as a plasticizer in the present invention has lower energy as compared to other conventionally used plasticizer such as nitroglycerine (NG), butanetriol trinitrate (BTTN), trimethylol ethane trinitrate (TMETN) and diethylene glycol dinitrate (DEGDN); can be decomposed at relatively low temperature; and is thermodynamically compatible with HTPE and HTPC which are used as a binder.

The BuNENA may be used at the amount of 5-15 wt % in the solid propellant composition according to the present invention. When the amount is less than 5 wt %, the specific impulse of the propellant becomes disadvantageously lowered, and when it is more than 15 wt %, the mechanical properties of the propellant at high temperature becomes disadvantageously weak.

The solid propellant composition of the present invention, in addition to BuNENA as a plasticizer, may further include at least one of TMETN and BTTN, which are conventionally used plasticizers. When further including at least one of TMETN and BTTN, the total amount of TMETN and/or BTTN is preferably 30% or less of the weight of the BuNENA.

As for AP which is used as a main oxidizer, any AP may be used without being specifically limited, and commercial AP, for example, AP200, AP6(produced by

) may be used, at the amount of 10-70 wt % in the solid propellant composition according to the present invention. When the amount is less than 10 wt %, oxygen in the propellant is not sufficient enough, which hinders the normal combustion disadvantageously, and it is more than 70 wt %, the propellant becomes sensitive to impact from outside, disadvantageously.

AN, which is used as a secondary oxidizer, is an oxidizer having relatively low decomposition temperature, and commercial AN, for example, AN150, AN50 (produced by

) and the like may be used. When the amount of AN is less than 1 wt %, sufficient effect is not obtained, and when it is more than 30 wt %, the performance of the propellant becomes degraded as well as the high hygroscopic property of AN which would have undesirable effects.

As for the component at least one selected from the group consisting of Al compounds, Zr compounds, Fe compounds and B compounds which is used as metal fuel in the solid propellant composition of the present invention, when it is used at the amount of less than 1 wt %, the desired effect cannot be sufficiently obtained, and when it is more than 30 wt %, the performance of the propellant becomes rather lowered and oxygen in the propellant is insufficient owing to the low content by percentage of oxidizer, disadvantageously.

The solid propellant composition of the present invention may further comprise additional additives which may be generally used in the conventional solid propellant composition. Especially, the following components may be further included in the solid propellant composition of the present invention at the amount of 0.1-1 wt %, respectively: as a curing agent, one or more selected from isophorone diisocyanate (IPDI), polyfunctional aliphatic isocyanate (commercial examples thereof include Desmodure®N-100 or Desmodure®N-3200 manufactured by Mobay Chem); as a binding agent, TEPANOL (product resulted from the reaction between tetraethylene penthamine nitrile (TEPAN) and glycidol); as a stabilizing agent, N-methyl-p-nitroaniline (NMA) or 2-nitrodiphenylamine (2NDPA).

According to the present invention, it is possible to provide a solid propellant which is insensitive to impact as well as thermal reactions and has desirable SCO characteristics in thermal reaction properties although it uses AP as a main oxidizer. Specifically, by the present invention, provided is an insensitive solid propellant composition having class 1.3 (0 card) of LGST test results, 15 MPa/ms or less of friability, excellent thermal reaction characteristics, i.e. SCO characteristics, wherein the reaction occurs at low temperature.

EMBODIMENT OF THE INVENTION Example

Hereinafter, the present invention is further illustrated through the following examples and comparative examples.

Tests regarding impact and thermal reactions in the examples and comparative examples were carried out by the following methods.

LSGT

LSGT refers to a large scale card gap test (LSGT) developed by US Naval ordnance laboratory (NOL), in which the reaction of a propellant to the energy delivered in the form of shock pressure is estimated. The shock pressure to be delivered to the specimen is generated by using detonation of a donor, i.e. an explosive, and adjusted by the gap between cards which are inserted between the explosive and specimen as a buffering material. As for the donor, Pentolite or Tetrile may be used, and as for the card material, wax, polymethylmethacrylate (PMMA), cellulose acetate and the like may be used.

When the card number is 70 or more (thickness 17.78 mm or more and shock pressure 31.74 Kbar or less), the hazard class is classified as class 1.1 at which detonation may occur. For manufacturing an insensitive solid rocket propellant, the propellant should obtain the result of at least class 1.3 (0 card).

Friability Test

The friability test was carried out by the method of UN Test series 7(c), wherein a propellant specimen in a cylindrical form having a diameter of 18 mm and a weight of 9 g was collided to a steel plate with a thickness of 20 mm at the speed of 150 m/s; the deformed propellant was collected; and then the collected propellant is combusted, by using a ignition bag composed of 0.5 g black, in a 108 cc-volume closed bomb in which pressure changes per time can be measured.

From the measured pressure change data, the pressure increase rate per unit time (dP/dt) was calculated and the maximum value was obtained. The standard value for passing the friability test according to UN Test series 7(c) was 15 MPa/ms or less that is the average value of the test results data, i.e. dP/dt maximum values, when tested at the collision speed of 150 m/s as above.

SCO Test

SCO test is to estimate the thermal insensitiveness of a sample, and carried out according to EID SCO test of UN Test series 7(f). After the test, when the number of broken pieces of tested metal pipe is not more than 2, it is determined to be acceptable, while the number is more than 2, it is determined to be unacceptable.

Other Tests

Other tests for determining combustion rate, pressure index, tensile strength, strain rate and density were carried out according to ADP-STD which refers to the standard analytic methods for propellant developed by the Agency for Defense development in Korea. Specifically, combustion rate and the pressure index were measured by ADP-STD-2008; tensile strength and strain rate were measured by ADP-STD-2004; and density was measured by ADP-STD-2002.

Example 1

A solid propellant composition composed of HTPE 6.5 wt %, N-3200 0.5 wt %, IPDI 0.3 wt %, BuNENA 10.8 wt %, AP 69.75 wt % (AP200 46 wt % and AP6 23.75 wt %), AN 10 wt % (AN150), ZrC 1.0 wt %, Fe₂O₃ 0.25 wt %, TEPANOL 0.15 wt %, NMA 0.5 wt % and 2NDPA 0.25 wt % was prepared.

The above-mentioned various test results of this composition were shown in Table 1.

9.85 mm/s of combustion rate at 1,000 psia (20° C.), 0.5334 of pressure index, 7.5 bar of tensile strength, 65% of strain rate, 20.2 bar of elastic modulus, 1.714 g/cc of density and 2 pieces from EIDS SCO test.

Example 2

A solid propellant composition composed of HTPE 6.5 wt %, N-3200 0.5 wt %, IPDI 0.3 wt %, BuNENA 10.8 wt %, AP 69.75 wt % (AP200 46 wt % and AP6 23.75 wt %), AN 10 wt % (AN50), ZrC 1.0 wt %, Fe₂O₃ 0.25 wt % TEPANOL 0.15 wt %, NMA 0.5 wt % and 2NDPA 0.25 wt % was prepared.

The above-mentioned various test results of this composition were shown in Table 1.

9.87 mm/s of combustion rate at 1,000 psia (20° C.), 0.5321 of pressure index, 9.7 bar of tensile strength, 59% of strain rate, 24 bar of elastic modulus, 1.715 g/cc of density and 2 pieces from EIDS SCO test.

Example 3

A solid propellant composition composed of HTPE 7.6 wt %, N-100 0.7 wt %, IPDI 0.4 wt %, BuNENA 10.4 wt %, AP 68.7 wt % (AP200 45 wt % and AP6 23.7 wt %), AN 10 wt % (AN50), ZrC 1.0 wt %, Fe₂O₃ 0.3 wt %, TEPANOL 0.15 wt %, NMA 0.5 wt % and 2NDPA 0.25 wt % was prepared.

The above-mentioned various test results of this composition were shown in Table 1.

9.92 mm/s of combustion rate at 1,000 psia (20° C.), 0.5342 of pressure index, 10.3 bar of tensile strength, 52% of strain rate, 29 bar of elastic modulus, 1.703 g/cc of density and 2 pieces from EIDS SCO test.

Example 4

A solid propellant composition composed of HTPE 7.5 wt %, N-3200 0.9 wt %, IPDI 0.3 wt %, BuNENA 10.4 wt %, AP 68.7 wt % (AP200 45 wt % and AP6 23.7 wt %), AN 10 wt % (AN50), ZrC 1.0 wt %, Fe₂O₃ 0.3 wt %, TEPANOL 0.15 wt %, NMA 0.5 wt % and 2NDPA 0.25 wt % was prepared.

The above-mentioned various test results of this composition were shown in Table 1.

9.89 mm/s of combustion rate at 1,000 psia (20° C.), 0.5340 of pressure index, 6.9 bar of tensile strength, 34% of strain rate, 27 bar of elastic modulus, 1.707 g/cc of density and 2 pieces from EIDS SCO test.

Example 5

A solid propellant composition composed of HTPE 6.5 wt %, N-3200 0.5 wt %, IPDI 0.3 wt %, BuNENA 10.8 wt %, AP 59.5 wt % (AP200 46 wt % and AP6 13.5 wt %), AN 20 wt % (AN50), ZrC 1.0 wt %, Fe₂O₃ 0.5 wt %, TEPANOL 0.15 wt %, NMA 0.5 wt % and 2NDPA 0.25 wt % was prepared.

The above-mentioned various test results of this composition were shown in Table 1.

9.18 mm/s of combustion rate at 1,000 psia (20° C.), 0.5422 of pressure index, 6.2 bar of tensile strength, 46% of strain rate, 18 bar of elastic modulus, 1.693 g/cc of density and 2 pieces from EIDS SCO test.

Example 6

A solid propellant composition composed of HTPE 7.4 wt %, N-3200 0.5 wt %, IPDI 0.3 wt %, BuNENA 9.9 wt %, AP 52.0 wt % (AP200 46 wt % and AP6 13.5 wt %), AN 10 wt % (AN50), A119 wt %, TEPANOL 0.15 wt %, NMA 0.5 wt % and 2NDPA 0.25 wt % was prepared.

The above-mentioned various test results of this composition were shown in Table 1.

8.32 mm/s of combustion rate at 1,000 psia (20° C.), 0.5663 of pressure index, 7.7 bar of tensile strength, 44% of strain rate, 29 bar of elastic modulus, 1.789 g/cc of density and 2 pieces from EIDS SCO test.

Example 7

A solid propellant composition composed of HTPE 6.3 wt %, HTPC 0.63 wt %, N-3200 0.8 wt %, IPDI 0.5 wt %, BuNENA 10.87 wt %, AP 68.7 wt % (AP200 45 wt % and AP6 23.7 wt %), AN 10 wt % (AN50), ZrC 1.0 wt %, Fe₂O₃ 0.3 wt %, TEPANOL 0.15 wt %, NMA 0.5 wt % and 2NDPA 0.25 wt % was prepared. HTCE was used at the amount of 10% based on the weight of HTPE.

The above-mentioned various test results of this composition were shown in Table 1.

8.86 mm/s of combustion rate at 1,000 psia (20° C.), 0.5331 of pressure index, 6.5 bar of tensile strength, 35% of strain rate, 29 bar of elastic modulus, 1.707 g/cc of density and 2 pieces from EIDS SCO test.

Example 8

A solid propellant composition composed of HTPC 6.8 wt %, N-3200 0.5 wt %, IPDI 0.3 wt %, BuNENA 11.5 wt %, AP 68.7 wt % (AP200 45 wt % and AP6 23.7 wt %), AN 10 wt % (AN50), ZrC 1.0 wt %, Fe₂O₃ 0.3 wt %, TEPANOL 0.15 wt %, NMA 0.5 wt % and 2NDPA 0.25 wt % was prepared. HTCE was used at the amount of 10% based on the weight of HTPE.

The above-mentioned various test results of this composition were shown in Table 1.

9.76 mm/s of combustion rate at 1,000 psia (20° C.), 0.5362 of pressure index, 8.1 bar of tensile strength, 38% of strain rate, 38 bar of elastic modulus, 1.713 g/cc of density and 2 pieces from EIDS SCO test.

Comparative Example 1

A solid propellant composition composed of HTPB 8.15 wt %, IPDI 1.5 wt %, dioctyl adipate (DOA) 3.0 wt %, AP 85.5 wt % (AP200 59.5 wt % and AP6 26 wt %), ZrC 1.5 wt %, TEPANOL 0.1 wt % and AO2246(2,2-methylene-bis(4-methyl-6-tert-butylphenol; antioxidant; produced by American cyanamid) 0.25 wt % was prepared.

The above-mentioned various test results of this composition were shown in Table 1.

13.25 mm/s of combustion rate at 1,000 psia (20° C.), 0.4628 of pressure index, 8.1 bar of tensile strength, 38% of strain rate, 38 bar of elastic modulus, 1.713 g/cc of density, 13 pieces from EIDS SCO test and 10.51 MPa/ms friability.

Comparative Example 2

A solid propellant composition composed of HTPE 7.0 wt %, N-3200 0.5 wt %, IPDI 0.3 wt %, BuNENA 10.8 wt %, AP 79.5 wt % (AP200 56 wt %, AP6 23.5 wt %), ZrC 1.0 wt %, Fe₂O₃ 0.5 wt % TEPANOL 0.15 wt %, NMA 0.25 wt % was prepared.

The above-mentioned various test results of this composition were shown in Table 1.

11.77 mm/s of combustion rate at 1,000 psia (20° C.), 0.4560 of pressure index, 8.2 bar of tensile strength, 55% of strain rate, 22.4 bar of elastic modulus, 1.739 g/cc of density, 11 pieces from EIDS SCO test and 9.39 MPa/ms friability.

Comparative Example 3

A solid propellant composition composed of HTPE 6.5 wt %, N-3200 0.5 wt %, IPDI 0.3 wt %, BuNENA 10.8 wt %, AP 79.5 wt % (AP200 66 wt %, AP6 13.5 wt %), ZrC 1.0 wt %, Fe₂O₃ 0.5 wt %, TEPANOL 0.15 wt %, NMA 0.5 wt %, 2NDPA 0.25 wt % was prepared.

The above-mentioned various test results of this composition were shown in Table 1.

11.54 mm/s of combustion rate at 1,000 psia (20° C.), 0.4430 of pressure index, 8.0 bar of tensile strength, 57% of strain rate, 23.4 bar of elastic modulus, 1.738 g/cc of density and 7 pieces from EIDS SCO test and 9.39 MPa/ms friability.

TABLE 1 SCO results Curing (excluding a LSGT Binder/plasticizer AP AN Stabilizer agent lid) Friability score Example 1 HTPE/BuNENA 69.75 10 0.75 IPDI 2 5.52 1.3 Example 2 HTPE/BuNENA 69.75 10 0.75 IPDI 2 5.91 1.3 Example 3 HTPE/BuNENA 68.7 10 0.75 IPDI 2 5.43 1.3 Example 4 HTPE/BuNENA 68.7 10 0.75 IPDI 2 5.55 1.3 Example 5 HTPE/BuNENA 59.5 20 0.75 IPDI 2 5.82 1.3 Example 6 HTPE/BuNENA 52.0 10 0.75 IPDI 2 5.12 1.3 Example 7 BuNENA 68.7 10 0.75 IPDI 2 5.20 1.3 Example 8 HTPC/BuNENA 68.7 10 0.75 IPDI 2 5.11 1.3 Comparative HTPB/DOA 85.5 0 0 IPDI 13 10.51 1.3 example 1 Comparative HTPE/BuNENA 79.5 0 0.25 IPDI 11 9.39 1.3 example 2 Comparative HTPE/BuNENA 79.5 0 0.75 IPDI 7 5.11 1.3 example 3

As seen from the above Table 1, the solid propellant compositions of the examples according to the present invention satisfy 2 or less pieces from SCO test, although AP was used as a main oxidizer, however, the compositions of the comparative examples which uses AP and a binder according to the present invention with the composition ratio being different from the present invention results in 3 or more pieces in SCO test, which do not satisfy the required level. 

1. An insensitive solid propellant composition comprising: 5-10 wt % of at least one selected from hydroxy-terminated polyether (HTPE) and hydroxy-terminated polycaprolactone ether (HTPC) as a binder; 5-15 wt % of N-butyl-N-(2-nitratorethyl)nitramine (BuNENA) as a plasticizer; 10-70 wt % of ammonium perchlorate (AP) as a main oxidizer; 1-30 wt % of ammonium nitrate (AN) as an auxiliary oxidizer; and 1-30 wt % of at least one selected from Al compounds, Zr compounds, B compounds and Fe compounds.
 2. The insensitive solid propellant composition according to claim 1, which comprises both of hydroxyl-terminated polyether and hydroxyl-terminated polycaprolactone ether as a binder.
 3. The insensitive solid propellant composition according to claim 1, which further comprises at least one of trimethylol ethane trinitrate and butanetriol trinitrate as a plasticizer.
 4. The insensitive solid propellant composition according to claim 1, which further comprises at least one isophorone diisocyanate and polyfunctional aliphatic isocyanate as a curing agent.
 5. The insensitive solid propellant composition according to claim 1, which further comprises N-methyl-p-nitroaniline or 2-nitrodiphenylamine. 